I have the fondest memories of consuming Shamrock Shakes when I was a wee lad in the '70s. Those were definitely the best.
I remember trying to get one several years ago, only to receive a rather blank (blanker, I guess) expression from the zitty, porcine-faced McD's cashier. Then, only like two years ago, my wife, after hearing my endless bleatings of how this delicious green concoction wasn't available any longer, told me there was a McD's up the road that had them advertised. Needless to say, I jumped in the truck and picked up the largest size they had.
It was totally not how I remembered it.
However, I may have to try to get a hold of another one this year just to make sure it wasn't just an off-day for the Shamrock Shake machine.